Dissatisfaction with the government has been growing over high levels of unemployment, a lack of basic services and allegations of widespread corruption.

Our correspondent says the ANC is likely to use its impressive mandate to try to drive through its National Development Plan - rejecting nationalisation, and emphasising investment and infrastructure.

The business-friendly plan has alarmed South Africa's powerful unions - some of which may soon break away to form their own party, he says.

He adds that, on 6%, the EFF are no threat to the ANC but their aggressive populism will keep ministers on their toes, and South African politics more abrasive than ever.

The DA has increased its share of the vote from 17% in the last election to 22%.

South Africa votes

About 25 million registered voters - half the population

Only a third of those born after 1994 registered

29 parties contested poll

ANC was defending 66% majority

DA was main challenger

Julius Malema formed new left-wing party, EFF, last year

About half the population lives on just over $2 (£1.5) a day

Source: IEC; IOL news site; government

Early on Thursday, DA leader Helen Zille told AFP news agency that she expected her party's final vote to be around the 23% margin.

"We'll see how it goes. Of course, we hope it will be more. We did as much as we could," she is quoted as saying.

The DA has been trying to make inroads into the black electorate - its support is mainly concentrated in the Western Cape which has a large white and mixed-race population.

Those born after the end of apartheid in 1994 were able to cast their ballots for the first time, although only a third of those entitled to do so had registered to vote.

An ANC victory would return President Jacob Zuma for a second five-year term. He was dogged by allegations of corruption in the build-up to the election after an independent inquiry found he had "unduly benefited" from an expensive government-funded upgrade to his private residence.

Speaking as he cast his vote on Wednesday, Mr Zuma said he thought "the results will be very good", but added that the campaign had been "very challenging".

In the last election in 2009, the ANC saw a slight drop in support, polling 66% of the vote.